The purpose of this four year project is to determine how much, how vigorous and what patterns of physical activity are necessary to maintain cardiovascular health among older women. Accelerometers will be used to characterize the amounts and patterns of physical activity. In a cohort of 8000 WHI participants aged 80 and older we will: 1) Determine the association of total volume of physical activity (light, moderate and vigorous) as measured by accelerometry with rates of incident CVD and total mortality; 2) Determine the associations of moderate-to-vigorous-intensity physical activity (MVPA) and sedentary time with rates of incident CVD and total mortality; 2.1) Conduct a calibration study designed to determine accelerometry thresholds for women aged 80 and older that distinguish sedentary from light activity and light activity from moderate to vigorous activity in order to make Aim 2 directly relevant to older women; 3) Compare the magnitude and independence of associations between accelerometer measures of physical activity and sedentary time, and self-reported measures of MVPA and sedentary time, with rates of incident CVD and total mortality; and 4) Determine associations of total volume of physical activity, MVPA and sedentary time with rates of fall-related injuries and overall risk for any injury. To accomplish these aims, 8,000 face-to-face visits will be conducted nationwide among women aged 80 and older from the Women's Health Initiative (WHI) who were originally enrolled between 1993-1997. Participants will wear an accelerometer for 7 days, complete a questionnaire containing the CHAMPS and WHI physical activity scales, and the Falls Efficacy Scale, and be followed through at least 2015 (3-4 years) to ascertain study outcomes. For the calibration study, two WHI clinics will recruit 200 women for participation in a clinic visit to measure energy expenditure during various activities using indirect calorimetry. This evidence is crucial for formulating evidence-based physical activity guidelines that pertain to the growing population of older women in the US and worldwide.